Co-rotating dual speed multi-screw extruder and processing method thereof

ABSTRACT

The disclosure discloses a co-rotating dual speed multi-screw extruder and a processing method thereof, the co-rotating dual speed multi-screw extruder enables a first screw and a second screw with the same outer diameter to co-rotate at different speed in a barrel, and the two screws wipe with each other, to achieve self-cleaning in processing; and circular arcs meshed with each other are respectively arranged between root diameters and top diameters of the two screws to form a first step structure and a second step structure, thus breaking an axial symmetry of a cross-sectional contour of the screws, and moreover, the first step structure and the second step structure are periodically meshed in a meshing zone in a staggered manner, so that a flow channel in the meshing zone is changed in a topological way, a strong elongation action and a strong disturbance action are effectively introduced in the meshing zone.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to the field of multi-screw extruder, andmore particularly, to a co-rotating dual speed multi-screw extruder anda processing method thereof.

Description of the Related Art

A co-rotating multi-screw extruder mainly comprises a barrel and aplurality of screws installed in an inner cavity of the barrel, whereina co-rotating twin-screw extruder is most widely used in the co-rotatingmulti-screw extruder. A working mode of an equal rotation speed of twoscrews is used in the traditional co-rotating twin-screw extruder, butdue to the left-right symmetry of left and right screws, the disturbancein a meshing zone is weak and even there is a relaxation effect, whichlimits a melting and plasticizing mixing effect of the co-rotatingtwo-screw extruder. The working mode of the existing co-rotatingmulti-screw extruder is changed from equal speed to dual speed. Althougha speed difference is introduced between the two screws and a part ofelongation force field effect is introduced, the strong disturbanceaction and the strong elongation action cannot be generated in themeshing zone. Therefore, the existing co-rotating two-screw extruderstill has limited improvement on the melting and plasticizing mixingeffects of materials.

BRIEF SUMMARY OF THE INVENTION

The present disclosure is intended to solve at least one of thetechnical problems existing in the prior arts, and provides aco-rotating dual speed multi-screw extruder and a processing methodthereof, a strong disturbance action and a strong elongation action canbe generated among a plurality of screws, and a melting and plasticizingmixing effect of the co-rotating dual speed multi-screw extruder onmaterials is improved.

On the first aspect of the present disclosure, a co-rotating dual speedmulti-screw extruder is provided, which comprises: a barrel, the barrelhaving an inner cavity and further having an opening; and a screwcombination, the screw combination being installed in the inner cavityof the barrel, and comprising a first screw and a second screw inco-rotating dual speed rotation, and the first screw and the secondscrew being intermeshed to create a meshing zone; a first step structurebeing arranged between a root diameter and a top diameter of the firstscrew; a second step structure being arranged between a root diameterand a top diameter of the second screw, and the first step structure andthe second step structure being meshed in the meshing zone in astaggered manner.

The co-rotating dual speed multi-screw extruder above has at least thefollowing beneficial effects: the first screw and the second screw withthe same outer diameter rotate co-rotationally at dual speed to enablethe two screws to wipe with each other to realize self-cleaning inprocessing; a first step structure and a second step structure arearranged between root diameters and top diameters of the two screws, andthe first step structure and the second step structure are meshed in themeshing zone in a staggered manner, so that a flow channel in themeshing zone is changed in a topological way, the strong elongationaction and the strong disturbance action in the meshing zone areeffectively introduced, and the melting and plasticizing mixing effectis improved; and meanwhile, the use of a kneading block is reducedbetween the two screws, thus greatly improving the self-cleaning,narrowing the distribution of materials in processing, and improving theefficiency.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the first screw and thesecond screw are arranged vertically or horizontally in the barrel, andouter edges of the first screw and the second screw are tangent to aninner wall of the barrel. The two screws can be arranged vertically orhorizontally in the barrel, and automatic matching can be performedaccording to a model of the barrel. Moreover, the two screws are alwayskept in meshing contact with each other, so that the self-cleaningfunction can be achieved, and the outer edges of the two screws aretangent to the inner wall of the barrel, so that the effect of promotinga stronger elongation action in the meshing zone is achieved.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the first screw has asingle-tip thread structure, and the second screw has a two-tip threadstructure.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the first screw and thesecond screw have the same outer diameter.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, a cross-sectional contourof the first screw comprises multiple curve arcs, and the multiple curvearcs on the cross-sectional contour of the first screw comprise multiplecircular arcs and multiple non-circular curve arcs; a cross-sectionalcontour of the second screw also comprises multiple curve arcs, and themultiple curve arcs on the cross-sectional contour of the second screwalso comprise multiple circular arcs and multiple non-circular curvearcs; a number of the multiple curve arcs on the cross-sectional contourof the second screw is twice that of the multiple curve arcs on thecross-sectional contour of the first screw; and the multiple curve arcson the cross-sectional contour of the first screw are asymmetrical, andthe multiple curve arcs on the cross-sectional contour of the secondscrew are centrosymmetric.

An unchanged cross-sectional structure is used in the two screws, sothat a manufacturing process of the screw is relatively simple, andmeanwhile, a symmetry between the two screws is avoided, and an axialsymmetry of a single screw is also avoided. Moreover, a cross-sectionalcontour of the first screw is completely asymmetric, and the melting andplasticizing mixing effect of the co-rotating dual speed multi-screwextruder can be improved by utilizing an asymmetric effect of the screw.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, a rotating speed ratio ofthe first screw to the second screw is 2. The dual speed rotation of thetwo screws is realized, and the materials are strongly stretched.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, edges of the first screwand the second screw are both of smooth spiral structures. Theco-rotating dual speed multi-screw extruder can realize completeself-cleaning in processing.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the meshing zonecomprises an upper meshing zone and a bottom meshing zone, and the firststep structure and the second step structure are meshed in a staggeredmanner in the upper meshing zone; and the first step structure and thesecond step structure are meshed side-by-side in the bottom meshingzone. Staggered and side-by-side meshing relationships of the stepstructures of the two screws are realized in the upper and bottommeshing zones, so that the strong elongation action and the strongdisturbance action in the meshing zone are effectively introduced.Moreover, the two screws rotate at a high speed, resulting in a lot ofheat, which accelerates a melting process of solid materials. Meanwhile,a positive displacement conveying efficiency and a solid conveyingefficiency can also be improved, the problem of unstable product qualitycaused by feed fluctuation of material components can be effectivelysolved, and an extrusion yield can be increased to a greater extent.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the screw combinationfurther comprises a third screw; and a structure of the third screw isthe same as that of the first screw or the second screw, and the firstscrew, the second screw and the third screw are meshed in a straightline.

If the structure of the third screw is the same as that of the firstscrew, the first screw, the second screw and the third screw areconnected in sequence; and if the structure of the third screw is thesame as that of the second screw, the second screw, the first screw andthe third screw are connected in sequence.

According to the co-rotating dual speed multi-screw extruder describedin the first aspect of the present disclosure, the opening comprises afeed port, an exhaust port and a discharge port. The materials enterthrough the feed port, the exhaust port is used for exhausting wastegas, and the materials are extruded from the discharge port aftermelting and plasticizing mixing.

On the second aspect of the present disclosure, a processing method of aco-rotating dual speed multi-screw extruder is provided, whichcomprises: co-rotating a first screw and a second screw at differentspeeds to push materials forward in an inner cavity of a barrel;generating heat to melt the materials, by the rotation of the firstscrew and the second screw, and meanwhile, a first step structurearranged on the first screw and a second step structure arranged on thesecond screw being meshed in a meshing zone to stir and forcibly peelthe materials, to make the materials become a melt; performingplasticizing mixing on the materials which become a melt under a strongelongation action and a strong disturbance action generated by periodicmeshing of the first step structure and the second step structure in themeshing zone in a staggered manner; extruding the materials which becomea melt out from an outlet stably; and achieving self-cleaning, by thefirst screw and the second screw wiping with each other.

The processing method of the co-rotating dual speed multi-screw extruderabove at least has the following beneficial effects: according to themethod, an acting force generated by the co-rotating dual speed rotationof the first screw and the second screw is used to push the materialsforward, the materials can be melted by the heat generated by thehigh-speed rotation of the first screw and the second screw, the firststep structure and the second step structure are meshed with each otherin the meshing zone in a staggered manner, thus strengthening stirringand forced peeling effects on the materials, and meanwhile, the firststep structure and the second step structure are periodically meshed inthe meshing zone in a staggered manner, and the strong elongation actionand the strong disturbance action are also generated, thus improving theplasticizing mixing effect on the materials which become a melt.Finally, complete self-cleaning is also realized between the first screwand the second screw.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described hereinafter with referenceto the drawings and the embodiments.

FIG. 1 is a structure diagram of a co-rotating dual speed two-screwextruder provided by a first embodiment of the present disclosure;

FIG. 2 is a structure diagram of different working zones of theco-rotating dual speed two-screw extruder provided by the firstembodiment of the present disclosure;

FIG. 3 is a diagram showing staggered meshing in an upper meshing zoneof the co-rotating dual speed two-screw extruder provided by the firstembodiment of the present disclosure;

FIG. 4 is a diagram showing side-by-side meshing in a bottom meshingzone of the co-rotating dual speed two-screw extruder provided by thefirst embodiment of the present disclosure;

FIG. 5 is a cross-sectional contour diagram of the co-rotating dualspeed two-screw extruder provided by the first embodiment of the presentdisclosure;

FIG. 6 is a structure diagram of a co-rotating dual speed triple-screwextruder provided in the second embodiment of the present disclosure;and

FIG. 7 is a structure diagram of the co-rotating dual speed triple-screwextruder provided in the third embodiment of the present disclosure.

DETAILED DESCRIPTION

A co-rotating multi-screw extruder mainly comprises a barrel and aplurality of screws installed in an inner cavity of the barrel, whereina co-rotating two-screw extruder is most widely used in the co-rotatingmulti-screw extruder. A working mode of a constant rotating speed of twoscrews is used in the traditional co-rotating two-screw extruder, butdue to the left-right symmetry of left and right screws, the disturbancein a meshing zone is weak and even there is a relaxation effect, whichlimits a melting and plasticizing mixing effect of the co-rotatingtwo-screw extruder. The working mode of the existing co-rotatingmulti-screw extruder is changed from equal speed to dual speed. Althougha speed difference is introduced between the two screws and a part ofelongation force field effect is introduced, a stronger disturbanceaction cannot be generated in the meshing zone and a stronger elongationaction cannot be provided. Therefore, the existing co-rotatingmulti-screw extruder still has limited improvement on the melting andplasticizing mixing effect.

The present disclosure discloses a co-rotating dual speed multi-screwextruder and a processing method thereof, the co-rotating dual speedmulti-screw extruder enables a first screw and a second screw with thesame outer diameter to co-rotate at dual speeds in a barrel, and the twoscrews wipe with each other, so as to realize self-cleaning inprocessing; and one or multiple arcs meshed with each other arerespectively introduced between root diameters and top diameters of thetwo screws to form a first step structure and a second step structure,thus breaking an axial symmetry of a cross-sectional contour of thescrew, and moreover, the first step structure and the second stepstructure are periodically meshed in a meshing zone in a staggeredmanner, so that a flow channel in the meshing zone is changed in atopological way, a strong elongation action and a strong disturbanceaction are effectively introduced in the meshing zone, and a melting andplasticizing mixing effect on materials is comprehensively improved.

This part will describe the specific embodiments of the presentdisclosure in detail, and the preferred embodiments of the presentdisclosure are shown in the drawings. The purpose of the drawings is tosupplement the description in the written part of the description withgraphics, so that people can intuitively and vividly understand eachtechnical feature and overall technical solution of the presentdisclosure, but the drawings cannot be understood as a limiting to theprotection scope of the present disclosure.

In the description of the present disclosure, it shall be understoodthat the description regarding orientations, such as the orientation orposition relationship indicated by “upper”, “bottom”, “front”, “rear”,“left”, “right”, refers to the orientation or position relationshipbased on the drawings, which is only used for facilitating thedescription of the present disclosure and the simplification ofdescription instead of indicating or implying that the indicated deviceor element must have a specific orientation and be constructed andoperated in a specific orientation. Therefore, the description regardingorientations cannot be understood as a limiting to the presentdisclosure.

In the description of the present disclosure, the meaning of severalrefers to be one or more, and the meaning of multiple refers to be morethan two. The meanings of greater than, less than, more than, etc. areunderstood as not including this number, while the meanings of above,below, within, etc. are understood as including this number. “the first”and “the second” “ ” are only used for the purpose of distinguishingtechnical features if any, and cannot be understood as indicating orimplying relative importance, implicitly indicating the number of theindicated technical features or implicitly indicating the order of theindicated technical features.

In the description of the present disclosure, unless otherwise clearlydefined, words such as “arrange”, “install”, “connect”, etc. should beunderstood broadly, and those skilled in the art can reasonablydetermine the specific meanings of the above words in the presentdisclosure in combination with the specific contents of the technicalsolution.

Referring to FIG. 1 to FIG. 5 , the first embodiment of the presentdisclosure provides a co-rotating dual speed multi-screw extruder, andwith reference to FIG. 1 , the co-rotating dual speed multi-screwextruder comprises a barrel 10, and the barrel 10 has an inner cavityand further has an opening 30; the co-rotating dual speed multi-screwextruder further comprises a screw combination 20, the screw combination20 is installed in the inner cavity of the barrel 10, and comprises afirst screw 21 and a second screw 22 in co-rotating dual speed rotation,and the first screw 21 and the second screw 22 are meshed with eachother to create a meshing zone; the first screw 21 and the second screw22 have the same outer diameter; a first step structure 211 is arrangedbetween a root diameter and a top diameter of the first screw 21; asecond step structure 221 is arranged between a root diameter and a topdiameter of the second screw 22, and the first step structure 211 andthe second step structure 221 are meshed in the meshing zone in astaggered manner; a rotating speed ratio of the first screw 21 to thesecond screw 22 is 2, and edges of the first screw 21 and the secondscrew 22 are both of smooth spiral structures; and in the embodiment,the first screw 21 and the second screw 22 form a flow channel 40 withthe inner cavity of the barrel 1, and the flow channel 40 is used forpassage of materials.

The first screw 21 and the second screw 22 are arranged vertically orhorizontally in the barrel 1, in FIG. 1 , the first screw 21 and thesecond screw 22 are preferably arranged vertically for display, it canbe understood that the first screw 21 and the second screw 22 can alsobe arranged horizontally, and the selection can be made according to anactual situation of the barrel 10. Outer edges of the first screw 21 andthe second screw 22 are tangent to an inner wall of the barrel 10.

The first screw 21 and the second screw 22 co-rotate at differentrotation speeds, so that the first screw and the second screw wipe witheach other to realize self-cleaning, the edges of the first screw 21 andthe second screw 22 are both of the smooth spiral structures, so thatthe use of a kneading block is reduced, and the self-cleaning isfacilitated to be improved, and moreover, step structures are arrangedbetween root diameters and top diameters of both screws, and the stepstructures of the two screws are meshed with each other in the meshingzone in a staggered manner, thus the flow channel 40 is changed in atopological way, and a strong elongation action and a strong disturbanceaction in the meshing zone are effectively introduced, thus improvingthe melting and plasticizing mixing effect of the co-rotating dual speedmulti-screw extruder.

Referring to FIG. 2 , the barrel 10 is further provided with a conveyingzone S1, a melting zone S2, an exhaust zone S3 and a mixing extrusionzone S4; in the conveying zone S1, for the melting zone S2, the exhaustzone S3 and the mixing extrusion zone S4, the processed materials movefrom S1 to S2 to S3 to S4, the conveying zone S1 is provided with a feedport 31 communicated with the outside, the exhaust zone S3 is providedwith an exhaust port 32 communicated with the outside, and a tail end ofthe mixing extrusion zone S4 is provided with a discharge port 33communicated with the outside.

Referring to FIG. 3 and FIG. 4 , the meshing zone comprises an uppermeshing zone and a bottom meshing zone, and the first step structure 211and the second step structure 221 are meshed in a staggered manner inthe upper meshing zone; and the first step structure 211 and the secondstep structure 221 are meshed side-by-side in the bottom meshing zone.Staggered and side-by-side meshing relationships of the step structuresof the two screws are realized in the upper and bottom meshing zones,and the strong elongation action and the strong disturbance action inthe meshing zone can be introduced, wherein, in the embodiment, when thefirst screw 21 and the second screw 22 are arranged horizontally, a topview is the upper meshing zone and a bottom view is the bottom meshingzone, and it can be understood that when the first screw 21 and thesecond screw 22 are arranged vertically, a front view is the uppermeshing zone and a rear view is the bottom meshing zone.

Referring to FIG. 5 , a single-tip thread structure is used in the firstscrew 21, a circular arc with a radius r_(M) is introduced into thecross-sectional contour of the first screw 21 to form the first steppedstructure 211, d/2<r_(M)<D/2, wherein d is inner diameters of the firstscrew 21 and the second screw 22, and D is maximum outer diameters ofthe first screw 21 and the second screw 22; a two-tip thread structureis used in the second screw 22, two circular arcs with a radius C−r_(M)are introduced into the cross-sectional contour of the second screw 22to form the second step structure 221, wherein C is a length of aconnecting line between a rotation center O₁ of the first screw 21 and arotation center O₂ of the second screw 22.

Referring to FIG. 5 , the maximum outer diameters of the first screw 21and the second screw 22 are D, the corresponding radius is R, the innerdiameters of the first screw 21 and the second screw 22 are d, thecorresponding radius is r, and then d=2C−D. The cross-sectional contourof the first screw 21 is formed by connecting six curve arcs, the sixcurve arcs are AB, BC, CD, DE, EF and FA in sequence, wherein BC, DE andFA are non-circular curve arcs, AB, CD and EF are circular arcs, thecircular arcs and non-circular curve arcs are always connected atintervals, and a central angle β₁ corresponding to the curve arc BC is:β₁=3ar cos (C/D),

an auxiliary angle ε₁ is introduced with O₁C used as a polar axis;taking a counterclockwise direction as a positive direction, the curvearc BC at a polar angle θ₁ is: θ₁=2ε₁+a tan((D sin ε₁)/(2C−D cos ε₁)),and a corresponding polar radius ρ(θ₁) is:ρ(θ₁)=√{square root over (C ²+(D/2)² −CD cos ε₁)}, a central angle β₂corresponding to the curve arc DE is:

$\beta_{2} = {{2{{arcos}\left( {\left( {C^{2} + \left( {C - r_{M}} \right)^{2} - \left( {D/2} \right)^{2}} \right)/\left( {2{C\left( {C - r_{M}} \right)}} \right)} \right)}} + {{atan}\left( {\left( \sqrt{\left( {2{C\left( {C - r_{M}} \right)}} \right)^{2} - \left( {C^{2} + \left( {C - r_{M}} \right)^{2} - \left( {D/2} \right)^{2}} \right)^{2}} \right)/\left( {C^{2} + \left( {D/2} \right)^{2} - \left( {C - r_{M}} \right)^{2}} \right)} \right)}}$an auxiliary angle ε₂ is introduced with O₁D used as a polar axis;taking a clockwise direction as a positive direction, the curve arc DEat a polar angle θ₂ is:

θ₂=2ε₂+a tan((D sin ε₂)/(2C−D cos ε₂)), a corresponding polar radius ρ(θ₂) is:

ρ(θ₂)=√{square root over (C²+(D/2)²−CD cos ε₂)}, a central angle β₃corresponding to the curve arc FA is:

$\beta_{3} = {{2{{arcos}\left( {\left( {C^{2} + \left( {D/2} \right)^{2} - r_{M}^{2}} \right)/{DC}} \right)}} + {{atan}\left( {\left( \sqrt{\left( {CD} \right)^{2} - \left( {C^{2} + \left( {D/2} \right)^{2} - \left( r_{M} \right)^{2}} \right)^{2}} \right)/\left( {C^{2} + \left( r_{M} \right)^{2} - \left( {D/2} \right)^{2}} \right)} \right)}}$

an auxiliary angle ε₃ is introduced with O₁F used as a polar axis;taking a clockwise direction as a positive direction, the curve arc FAat a polar angle θ₃ is:

θ₃=2ε₃+a tan ((C−r_(M)) sin ε₃/(C−(C−r_(M))cos ε₃)), a correspondingpolar radius ρ(θ₃) is:ρ(θ₃)=√{square root over (C ²+(C−r _(M))²−2C(C−r _(M))cos ε₃)}

wherein r_(M) is a radius of the circular radius corresponding to thefirst step structure 211, and d/2<r_(M)<D/2. The three arcs arerespectively AB, CD and EF, the corresponding radii are d/2, D/2 andr_(M), the corresponding center angles are respectively α, γ and ϕ, thecenter angle ϕ meets α+γ+ϕ=2π−β₁−β₂−β₃, wherein the arc EF forms thefirst step structure 211.

A number of the multiple curve arcs on the cross-sectional contour ofthe second screw 22 is twice that of the multiple curve arcs on thecross-sectional contour of the first screw 21. As shown in FIG. 5 ,points A and A₁ are coincident, the cross-sectional contour of thesecond screw 22 is formed by connecting twelve curve arcs, which areA₁B₁, B₁C₁, C₁D₁, D₁E₁, E₁F₁ and F₁A₂, as well as A₂B₂, B₂C₂, C₂D₂,D₂E₂, E₂F₂ and F₂A₁ in sequence. The curve arcs A₁B₁, B₁C₁, C₁D₁, D₁E₁,E₁F₁ and F₁A₂ are centrosymmetric with the curve arcs A₂B₂, B₂C₂, C₂D₂,D₂E₂, E₂F₂ and F₂A₁ about the rotation center of the second screw 22,and the circular arcs and the non-circular curve arcs are alwaysconnected at intervals. B₁C₁, D₁E₁ and F₁A₂ are non-circular curve arcs,and the corresponding central angles are respectively β₁/2, β₂/2 andβ₃/2; and similarly, the central angles corresponding to non-circularcurve arcs B₂C₂, D₂E₂ and F₂A₁ are respectively β₁/2, β₂/2 and β₃/2.Moreover, the three circular arcs are respectively A₁B₁, C₁D₁ and E₁F₁,the corresponding radii are respectively d/2, D/2 and C−r_(M), and thecorresponding center angles are respectively α/2, γ/2 and ϕ/2.Similarly, the other three circular arcs are respectively A₂B₂, C₂D₂ andE₂F₂, the corresponding radii are respectively d/2, D/2 and C−r_(M), andthe corresponding center angles are respectively α/2, γ/2 and ϕ/2. Thecircular arcs E₁F₁ and E₂F₂ are the second step structures 221.Therefore, in the embodiment, the cross-sectional contours of the firstscrew 21 and the second screw 22 are unchanged, the multiple curve arcsof the cross-sectional contour of the first screw 21 are asymmetrical,and the multiple curve arcs of the cross-sectional contour of the secondscrew 22 are centrosymmetric about the rotation center. An unchangedcross-sectional contour is used in the two screws, so that amanufacturing process of the screw is relatively simple, and meanwhile,a symmetry between the two screws is avoided, and an axial symmetry of asingle screw is also avoided. Moreover, a cross-sectional contour of thefirst screw is completely asymmetric, and the melting and plasticizingmixing effect of the co-rotating dual speed multi-screw extruder can beimproved by utilizing an asymmetric effect of the screw. It can beunderstood that, in the embodiment, the cross-sectional contour of thefirst screw 21 comprises three circular arcs and three non-circularcurve arcs, and the cross-sectional contour of the second screw 22comprises six circular arcs and six non-circular curve arcs, which isonly the preferred solution; and in practical application, thecross-sectional contour of the first screw 21 can comprise N circulararcs and N non-circular curve arcs, and the cross-sectional contour ofthe second screw 22 can comprise 2N circular arcs and 2N non-circularcurve arcs, wherein N can be any number on the premise of ensuring thenormal use of the first screw 21 and the second screw 22.

Referring to FIG. 2 , a processing method for materials in a co-rotatingdual speed two-screw extruder in the embodiment comprises the followingsteps.

After the materials enter the flow channel of the conveying zone S1 fromthe feed port 31, the first screw 21 and the second screw 22respectively rotate co-rotationally at different speeds about the screwaxes to generate a conveying force; and meanwhile, the first stepstructure 211 and the second step structure 221 are meshed in astaggered manner in the upper meshing zone and side-by-side in thebottom meshing zone, thus increasing an axial positive displacementconveying force, and the materials move to the melting zone S2 under theaction of the conveying force and the combined action of a frictionforce between the two screws.

When the materials flow to the flow channel of the melting zone S2, dueto the heat generated by the high-speed rotation of the two screws andthe staggered meshing of the step structures, the materials are forciblymelted at a thrust surface position of the first screw 21 and a draggingsurface position of the second screw 22, and with staggered and parallelperiodic changes of the first step structure 211 and the second stepstructure 221 in the upper and bottom meshing zones, and the materialsare stirred and forcibly peeled, thus promoting an interface updatingeffect, strengthening a heat transfer process, accelerating a meltingprocess of the solid materials, and enabling the materials to become amelt.

After the materials which become a melt enter the flow channel of theexhaust zone S3 from the flow channel of the melting zone S2, pushingand scraping actions formed by the meshing of the first step structure211 and the second step structure 221 with each other promote theinterface updating and expand an exhaust area, and a negative pressureaction is generated by the materials collected here, thus acceleratingthe exhaust gas to be discharged from the exhaust port, while the moltenmaterials continue to be move towards the flow channel direction of themixing extrusion zone S4.

After the materials which become a melt enter the flow channel of themixing extrusion zone S4, the first screw 21 and the second screw 22 aremeshed and operated co-rotationally at different speeds, i.e., the speedratio of 2, the first step structure 211 and the second step structure221 are also meshed with each other in a staggered manner, the moltenmaterials are subjected to a periodic action in a process of movingtowards the discharge port 33, and the strong elongation action and thestrong disturbance action in the meshing zone, and are also subjected tothe action of different topological flow channel mechanisms, thusimproving the plasticizing mixing effect and enabling the materialswhich become a melt to be stably extruded from the discharge port, andmeanwhile, the first screw 21 and the second screw 22 wipe with eachother, so as to realize complete self-cleaning.

Referring to FIG. 6 , in the second embodiment of the presentdisclosure, a co-rotating dual speed triple-screw extruder is provided,different from the first embodiment, the screw combination 20 furthercomprises a third screw 23, the third screw 23 has the same structure asthe first screw 21 in the first embodiment, and the first screw 21, thesecond screw 22 and the third screw 23 are meshed in a “straight line”in sequence.

Referring to FIG. 7 , in the third embodiment of the present disclosure,a co-rotating dual speed triple-screw extruder is provided, differentfrom the first embodiment, the screw combination 20 further comprises athird screw 23, the third screw 23 has the same structure as the secondscrew 22 in the first embodiment, and the second screw 22, the firstscrew 21 and the third screw 23 are meshed in a “straight line” insequence.

The embodiments of the disclosure are described in detail above withreference to the drawings, but the disclosure is not limited to theembodiments above, and various changes may be made within the scope ofknowledge possessed by those of ordinary skills in the technical fieldwithout departing from the purpose of the disclosure.

What is claimed is:
 1. A co-rotating dual speed multi-screw extruder,comprising: a barrel, having an inner cavity and an opening; and a screwcombination, being installed in the inner cavity of the barrel, andcomprising a first screw and a second screw, which co-rotating atdifferent rotation speed, and the first screw and the second screw beingintermeshed to create a meshing zone; wherein a first step structurebeing arranged between a root diameter and a top diameter of the firstscrew, and a second step structure being arranged between a rootdiameter and a top diameter of the second screw, the first stepstructure and the second step structure being meshed in the meshing zonein a staggered manner; wherein a cross-sectional contour of the firstscrew comprises multiple curve arcs, and the multiple curve arcs on thecross-sectional contour of the first screw comprise multiple circulararcs and multiple non-circular curve arcs; wherein a cross-sectionalcontour of the second screw further comprises multiple curve arcs, andthe multiple curve arcs on the cross-sectional contour of the secondscrew also comprise multiple circular arcs and multiple non-circularcurve arcs; wherein a number of the multiple curve arcs on thecross-sectional contour of the second screw is twice that of themultiple curve arcs on the cross-sectional contour of the first screw;wherein the multiple curve arcs on the cross-sectional contour of thefirst screw are asymmetrical, and the multiple curve arcs on thecross-sectional contour of the second screw are centrosymmetric; andwherein a rotating speed ratio of the first screw to the second screw is2.
 2. The co-rotating dual speed multi-screw extruder according to claim1, wherein the first screw and the second screw are arranged verticallyor horizontally in the barrel, and outer edges of the first screw andthe second screw are tangent to an inner wall of the barrel.
 3. Theco-rotating dual speed multi-screw extruder according to claim 1,wherein the first screw has a single-tip thread structure, and thesecond screw has a two-tip thread structure.
 4. The co-rotating dualspeed multi-screw extruder according to claim 1, wherein the first screwand the second screw have a same outer diameter.
 5. The co-rotating dualspeed multi-screw extruder according to claim 1, wherein the meshingzone comprises an upper meshing zone and a bottom meshing zone, whereinin the upper meshing zone the first step structure and the second stepstructure are meshed in the staggered manner, and wherein in the bottommeshing zone the first step structure and the second step structure aremeshed side-by-side.
 6. The co-rotating dual speed multi-screw extruderaccording to claim 1, wherein the screw combination further comprises athird screw; and a structure of the third screw is a same as that of thefirst screw or the second screw, and the first screw, the second screwand the third screw are meshed in a straight line.
 7. The co-rotatingdual speed multi-screw extruder according to claim 1, wherein theopening comprises a feed port, an exhaust port and a discharge port. 8.A processing method of a co-rotating dual speed multi-screw extruder,comprising: rotating a first screw and a second screw co-rotationally atdual speeds to push materials forward in an inner cavity of a barrel;generating heat to melt the materials, by the rotating of the firstscrew and the second screw, and meanwhile, a first step structurearranged on the first screw and a second step structure arranged on thesecond screw being meshed in a meshing zone to stir and forcibly peelthe materials, to make the materials become a melt; wherein across-sectional contour of the first screw comprises multiple curvearcs, and the multiple curve arcs on the cross-sectional contour of thefirst screw comprise multiple circular arcs and multiple non-circularcurve arcs; wherein a cross-sectional contour of the second screw alsocomprises multiple curve arcs, and the multiple curve arcs on thecross-sectional contour of the second screw also comprise multiplecircular arcs and multiple non-circular curve arcs; wherein a number ofthe multiple curve arcs on the cross-sectional contour of the secondscrew is twice that of the multiple curve arcs on the cross-sectionalcontour of the first screw; wherein the multiple curve arcs on thecross-sectional contour of the first screw are asymmetrical, and themultiple curve arcs on the cross-sectional contour of the second screware centrosymmetric; and wherein a rotating speed ratio of the firstscrew to the second screw is 2; performing plasticizing mixing on thematerials which become a melt under a strong elongation action and astrong disturbance action generated by periodic meshing of the firststep structure and the second step structure in the meshing zone in astaggered manner; extruding the materials which become a melt out froman outlet stably; and realizing self-cleaning, by the first screw andthe second screw wiping with each other.